Finding Nemo is getting harder as climate change makes the fish infertile, according to new research.

The homes of the clownfish that inspired the hit movie are being destroyed by warming seas in the South Pacific.

It's stressing the colourful creatures out and reducing their sex drive, decimating numbers of offspring by three quarters, warn scientists.

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The homes of the clownfish that inspired the hit movie are being destroyed by warming seas in the South Pacific. It's stressing the colourful creatures out and reducing their sex drive, decimating numbers of offspring by three quarters, warn scientists

THE STUDY

Every other day for 14 months, from October 2015 to December 2016, researchers visited 13 pairs of clownfish and their host anemones off the coast of Moorea Island in French Polynesia.

This happened before, during, and after the El Nino event that in 2016 warmed Moorea Island by 2°C.

Half of the anemones bleached as they lost their microalgae.

Among the clownfish living there the number of viable eggs fell by a drastic 73 per cent.

These fish were laying eggs less frequently and they were also laying fewer and less viable eggs - unlike those housed by unbleached anemones where there was no change.

Blood samples taken from 52 pairs of clownfish, including the 13 original individuals showed a sharp increase levels of the stress hormone cortisol and a significant drop in male and female sex hormones - the equivalents of testosterone and oestrogen.

A study off the coast of Moorea Island in French Polynesia found they laid far fewer eggs after its host anemones became bleached last year.

Clownfish, also known as anemonefish, use the soft bodied animals that attach themselves to coral reefs to shelter in for protection against predators.

Bleaching is a well-known problem in corals, but it can also happen to sea anemones during heat waves.

Professor Suzanne Mills, of EPHE PSL Research University, Moorea, said: 'While no effects on adult anemone survival were observed, the effects of bleaching on reproduction and population demography were likely even greater than demonstrated here.'

She said the finding is alarming with manmade stressors and the rate of change in environmental conditions expected to multiply in the coming decades, 'with bleaching and habitat degradation becoming more frequent.'

Professor Mills added: 'Understanding whether individuals and populations can adjust their physiology and behaviour fast enough, either plastically or through evolutionary change, is a priority in conservation physiology.'

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The golden colour of the anemones is due to the microalgae present in their tentacles.

But warming causes the microalgae living in harmony with the corals to be ejected, which causes them to bleach.

Clownfish protect themselves from predators by sheltering among the anemones' tentacles, and each month lay eggs at their base.

Thankfully, clownfish - such as Nemo from the Pixar blockbuster, Finding Nemo, have a fairly long life, meaning researchers can monitor individuals over long periods of time

Clownfish protect themselves from predators by sheltering among the anemones' tentacles, and each month lay eggs at their base. Equally, the anemones are also protected by the clownfish that they host

OTHER SPECIES AFFECTED

The clownfish are not an isolated case with 12 per cent of the coastal fish in French Polynesia dependent on anemones or corals to feed or to find protection from predators.

In cases of prolonged bleaching, like that of the Australian Great Barrier Reef in 2016 and 2017, the renewal of all of these populations could be affected, and with them the stability of the ecosystems.

Professor Mills said at least 51 species of fish rely on sea anemones worldwide.

She said: 'We predict other species and taxa associated with sea anemones and corals will respond similarly to bleaching events, translating into significant losses in reproductive output.'

Equally, the anemones are also protected by the clownfish that they host.

Every other day for 14 months, from October 2015 to December 2016, researchers and students visited 13 pairs of clownfish and their host anemones in the coral reefs of the volcanic island famed for its sandy beaches.

This happened before, during, and after the El Nino event that in 2016 warmed Moorea Island by 2°C.

Half of the anemones bleached as they lost their microalgae.

Among the clownfish living there the number of viable eggs fell by a drastic 73 per cent.

These fish were laying eggs less frequently and they were also laying fewer and less viable eggs - unlike those housed by unbleached anemones where there was no change.

Blood samples taken from 52 pairs of clownfish, including the 13 original individuals showed a sharp increase levels of the stress hormone cortisol and a significant drop in male and female sex hormones - the equivalents of testosterone and oestrogen.

Blood samples taken from 52 pairs of clownfish, including the 13 original individuals showed a sharp increase levels of the stress hormone cortisol and a significant drop in male and female sex hormones - the equivalents of testosterone and oestrogen

The researchers said: 'The bleaching of the anemones due to increased sea surface temperatures is thus a stressor that reduces the levels of sex hormones and thus the fertility of the fish.

'These links have been found for the first time in the natural environment in which the fish live.'

The health of the anemones and the fish improved between three and four months after the end of the warming event, long after the temperatures had returned to normal.

This map shows the distribution of the seven unbleached (blue points) and six bleached (red points) anemone locations with breeding in the study

But the team fear this would not have been the case had the warming episode been more intense, or longer.

And, faced with a new warming episode, they also wonder if the clownfish that have already suffered this initial stress will be better acclimatised, or on the contrary more fragile.

The study published in Nature Communications is one of the first to attribute hormonal stress responses to climate change in the wild.

'These findings suggest hormone stress responses play a crucial role in changes to population demography following climate change and plasticity in hormonal responsiveness may be a key mechanism enabling individual acclimation to climate change.'

CLOWNFISH FATHERS HAVE STRONG NURTURING INSTINCTS BECAUSE OF A 'LOVE HORMONE'

One area where Finding Nemo had things right is the great lengths clownfish dads go to to support their offspring, just like Marlin.

Their parenting instincts are so strong that even if you place clownfish eggs from an unrelated nest near a bachelor anemonefish, he will take care of them.

Researchers previously found the love hormone behind this fathering behaviour.

And it's very similar to oxytocin, the hormone that facilitates bonding between human mothers and their babies after childbirth.

Scientists, based at the University of Illinois at Urbana-Champaign, decided to study the brain chemistry behind this parental care.

So they took individual anemonefish that were fathering and gave them an injection of antagonists.

They then analysed how these drugs might either promote or inhibit male parental care.

They found that anemonefish rely on isotocin, a signalling molecule that is almost identical to oxytocin.

When the researchers blocked this hormone, they found that the anemonefish fathers stopped tending to their eggs.

The researchers have decided to continue to monitor each individual during the next El Nino episode - made possible due to the fact clownfish have a fairly long life expectancy and are sedentary, moving very little from their host anemone.

The complex and natural weather event is marked by an upwelling of warm water in the Pacific.

The 'Super El Nino' of 2016 is said to have had a role in driving global temperatures to record highs.

A study off the coast of Moorea Island in French Polynesia found they laid far fewer eggs after its host anemones became bleached last year

The clownfish are not an isolated case with 12 per cent of the coastal fish in French Polynesia dependent on anemones or corals to feed or to find protection from predators.

In cases of prolonged bleaching, like that of the Australian Great Barrier Reef in 2016 and 2017, the renewal of all of these populations could be affected, and with them the stability of the ecosystems.

Professor Mills said at least 51 species of fish rely on sea anemones worldwide.

She said: 'We predict other species and taxa associated with sea anemones and corals will respond similarly to bleaching events, translating into significant losses in reproductive output.'